Silicon wafer polishing by CMP allows highly precise planarizing to be achieved by multiple steps of, i.e., three or four steps of polishing. The primary polishing and the secondary polishing conducted in the first and second steps are mainly intended for surface planarizing and require high polishing speeds.
In order to achieve a high polishing speed, the shape or size of abrasives or the amount of addition is varied or a basic compound is added. A polishing agent disclosed by Patent Document 1 allows the polishing speed to be improved by optimizing the shape of colloidal silica and its specific surface area.
Not only the high polishing speed is required but also the surface roughness of a polished wafer must be reduced, and the surface roughness is improved by adding a surfactant or an organic compound. A polishing composition disclosed by Patent Document 2 includes a polishing agent and, as an additive, at least one compound selected from the group consisting of a hydroxide of an alkali metal, a carbonate of an alkali metal, a hydrogencarbonate of an alkali metal, a quaternary ammonium salt, a peroxide, and a peroxy acid compound, so that a planarized polished surface can be formed and a higher polishing speed can be obtained.
As the multi-step polishing has come to be carried out as general process in order to provide a wafer planarized with high precision, the difference between finishing polishing in the final steps such as the third and fourth steps and the secondary polishing has diminished, and polishing characteristics similar to the finishing polishing have been requested also in the secondary polishing.
As the performance of evaluation equipment improves, evaluation items used for the finishing polishing can be applied in evaluation in the secondary polishing, and for example the same items as those in the finishing polishing such as reduction in LPD (light point defects) and improvement in defoaming properties are requested in the secondary polishing.
A polishing composition disclosed by Patent Document 3 includes at least one selected from a block polyether including an oxyethylene group and an oxypropylene group, silicon dioxide, a basic compound, hydroxyethyl cellulose and a polyvinyl alcohol and water, so that COP (Crystal Originated Particle) and haze levels are improved.